In the oceaneering field, a floating production storage and offloading system (FPSO for short) is an offshore oil and gas processing system integrating oil and gas processing, oil storage and offloading, heat supply, power generation, control and life functions, which has gradually become a mainstream mode for offshore oilfield development in the world owning to the advantages of strong oil storage capability, wide applicability and the like.
Generally, the FPSO system mainly comprises floating main body, mooring and positioning system, oil storage and transport module, oil and gas processing module, living support module and other multiple modules, which are essential facilities for technology-intensive and capital-intensive offshore oil development. Wherein, the kinetic characteristic, structural strength, oil storage efficiency, construction cost, operation cost, safety and other properties of the FPSO system depend on the appearance of the floating body.
The traditional FPSO systems are generally transformed from old oil tankers or are barge-like FPSO systems designed and built in accordance with standard shipping ideas. However, those ship-like floating bodies have some limitations and shortages in the appearance as follows:
1. The natural heave period of the traditional ship-like FPSO is hardly away from a wave energy concentration area, and the heave movement amplitude is relatively large. Besides, the ship-like FPSO is very sensitive to the action direction of waves and has overlarge area of transverse motion in heading sea, thus resulting in relatively poor sway movement performances, all of which will seriously affect normal work of various equipments and instruments of FPSO as well as quality of produced raw oil and comfortable level of staff.
2. The traditional ship-like FPSO has a 360-degree all-sided freely-rotating wind indicator effect due to a single-point mooring system equipped with an inner turret and a fluid connector, however, serious yaw movement will not only affect normal running of many works, but will wear the inner turret and the fluid connector to make them frequent in need of repair and maintenance. Therefore, the production cost will be greatly increased due to self exorbitant prices of the inner turret and the fluid connector and existence of potential downtime.
3. The traditional ship-like FPSO has relatively large longitudinal size and very large corresponding longitudinal hogging and sagging bending loads, which makes the floating body easily suffer bending and fatigue rupture. Particularly for FPSO transformed from old ships, the fatigue phenomenon is especially serious. Therefore, in order to meet the requirements on strength and fatigue load, load reinforcement needs to be performed generally, and accordingly, the construction cost of FPSO is increased.
4. The length and the layout difficulty of a connecting piping system among numerous functional modules will be increased by the slender floating body and the deck of the traditional ship-like FPSO, and accordingly, the construction cost and the maintenance cost are increased potentially.
Moreover, the cylindrical FPSO main body is of a floating cylindrical structure moored at the bottom of the sea. Such structure has large-scale storage, oil and gas production capabilities, is not sensitive to the directivity of wind, wave and current and has relatively small yaw movement amplitude, and whereas it has many shortages in terms of performances: large heave movement amplitude of the floating body, vortex-induced vibration, and the living space is too close to the working space by reason of relatively small deck area, which is not advantageous to separating a danger area from a non-danger area.